Wireless ECG in implantable devices

ABSTRACT

An implantable medical device such as an implantable pacemaker or implantable cardioverter/defibrillator includes a programmable sensing circuit providing for sensing of a signal approximating a surface electrocardiogram (ECG) through implanted electrodes. With various electrode configurations, signals approximating various standard surface ECG signals are acquired without the need for attaching electrodes with cables onto the skin. The various electrode configurations include, but are not limited to, various combinations of intracardiac pacing electrodes, portions of the implantable medical device contacting tissue, and electrodes incorporated onto the surface of the implantable medical device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to co-pending, commonly assigned U.S. patentapplication Ser. No. 10/712,776, entitled “IMPLANTABLE CARDIAC MONITORUPGRADEABLE TO PACEMAKER OR CARDIAC RESYNCHRONIZATION DEVICE,” filed onNov. 13, 2003, and U.S. patent application Ser. No. 10/746,855, entitled“WIRELESS ECG PACE AVOIDANCE AND DISPLAY METHOD,” filed on Dec. 24,2003, which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

This document generally relates to cardiac rhythm management (CRM)systems and particularly, but not by way of limitation, to such systemsusing an implantable medical device to sense a signal that approximatesa surface electrocardiogram (ECG).

BACKGROUND

The heart is the center of a person's circulatory system. It includes acomplex electro-mechanical system that draws oxygenated blood from thelungs and pumps it to the organs of the body to provide the organs withtheir metabolic needs for oxygen, and draws deoxygenated blood from theorgans and pumps it into the lungs where the blood gets oxygenated. In aheart having a normal electrical system, the sinoatrial node, theheart's natural pacemaker, generates electrical signals, called actionpotentials, that propagate through an electrical conduction system tovarious regions of the heart to excite myocardial tissues in theseregions. Coordinated delays in the propagations of the action potentialsin a normal electrical conduction system cause the various regions ofthe heart to contract in synchrony such that the pumping functions areperformed efficiently. The function of the electrical system isindicated by a biopotential signal sensed with at least two electrodesattached on the skin or implanted in the body. When the electricalsystem functions abnormally, the biopotential signal shows thatcontractions at one or more cardiac regions are chaotic andasynchronized. Such conditions are known as cardiac arrhythmias. Timingand morphological information contained in the biopotential signal isused to diagnose the type of arrhythmia and/or determine an appropriatetherapy.

When the biopotential signal is sensed with electrodes attached onto theskin, the sensed signal is commonly referred to as surfaceelectrocardiogram (ECG), or simply ECG. Various standard ECG signals(vectors) are recorded for diagnostic purposes with differentcombinations of electrode locations. When the electrodes are implantedunderneath the skin, the sensed signal is referred to as subcutaneousECG or far-field electrogram. When at least one electrode is placed inor on the heart, the sensed signal is referred to as electrogram orintracardiac electrogram. Surface ECG is widely used for diagnosticpurposes and provides for information on the global electricalperformance of the heart. Subcutaneous ECG is known to closelyapproximate the surface ECG. In contrast, intracardiac electrogramindicates localized electrical performance and may not containsufficient information for general diagnostic purposes. Implantablemedical devices such as cardiac pacemakers andcardioverter/defibrillators sense intracardiac electrograms for timingthe delivery of therapeutic electrical energy. Though such animplantable medical device is capable of acquiring intracardiacelectrograms and transmitting the electrograms for display in anexternal device, physicians may still need the surface ECG fordiagnostic and therapeutic purposes. The skin contact electrodes and thecables connecting the electrodes to an ECG recorder, as required forrecording the surface ECG, may become cumbersome, for example, during anoperation such as the implantation of the implantable medical device orduring a patient examination where ECG is recorded during exercise.Regular in-home ECG monitoring may be impractical in the absence of aphysician or other trained caregiver.

While studies have shown that signals acquired with implanted electrodesof certain configurations approximate surface ECG signals, there is aneed to implement a system to acquire a signal substituting for variousstandard surface ECG signals using an implantable medical device.

SUMMARY

A CRM system includes an implantable medical device such as animplantable pacemaker or implantable cardioverter/defibrillator. Theimplantable medical device includes a programmable sensing circuitproviding for sensing of a signal approximating a surface ECG throughimplanted electrodes. With various electrode configurations, signalsapproximating various standard surface ECG signals are acquired withoutthe need for attaching electrodes with cables onto the skin.

In one embodiment, a CRM system includes a plurality of implantableelectrodes and an implantable device. The implantable electrodes includeat least a first electrode and a second electrode selectable for sensinga cardiac signal approximating a surface ECG. The implantable medicaldevice includes a sensing circuit, a processor, and a programmable senseinterface. The sensing circuit includes a first sense input and a secondsense input being a pair of differential inputs for sensing the cardiacsignal approximating the surface ECG. The gain of the sensing circuit isprogrammable for at least a surface ECG gain selectable for sensing thecardiac signal approximating the surface ECG and an electrogram gainselectable for sensing an intracardiac electrogram. The frequencyresponse of the sensing circuit is programmable for at least a surfaceECG pass band selectable for sensing the cardiac signal approximatingthe surface ECG and an intracardiac electrogram pass band selectable forsensing an intracardiac electrogram. The processor controls theoperation of the sensing circuit. It includes a command receiver toreceive an ECG acquisition command. The programmable sense interfaceprovides at least a first electrical connection and a second electricalconnection in response to the ECG acquisition command. The firstelectrical connection connects the first electrode to the first senseinput. The second electrical connection connects the second electrode tothe second sense input.

In one embodiment, a CRM system includes a plurality of implantableelectrodes and an implantable medical device. The plurality ofimplantable electrodes are incorporated onto the implantable medicaldevice and configured for sensing cardiac signals each approximating asurface ECG vector. The implantable medical device includes a sensingcircuit, a processor, and a programmable sense interface. The sensingcircuit includes a plurality of sensing channels providing forsimultaneous sensing of the cardiac signals. The processor controls theoperation of the sensing circuit. It includes a command receiver toreceive an ECG acquisition command. The programmable sense interfaceprovides a plurality of pairs of electrical connections. Each pairconnects between one of the plurality of sensing channels and twoelectrodes selected from the plurality of implantable electrodes.

In one embodiment, an implantable medical device includes a sensingcircuit, a hermetically sealed can, and at least two concentricelectrodes. The sensing circuit is programmable for a frequency responsesuitable for sensing a surface ECG, and includes a first sense input anda second sense input being a pair of differential inputs for sensing acardiac signal. The hermetically sealed can houses a circuit includingat least portions of the sensing circuit. The can has an outer surfacesubject to contact with body tissue. The concentric electrodes areincorporated onto the outer surface of the can. These concentricelectrodes include at least an inner electrode and an outer electrode.The inner is coupled to the first sense input. The outer electrode iscoupled to the second sense input.

In one embodiment, a method provides for acquisition of a signalapproximating a surface ECG using an implantable medical device. Theacquisition starts in response to receiving an ECG acquisition command.A pass band of a sensing circuit of the implantable medical device isprogrammed for a surface ECG pass band. A sense interface of theimplantable medical device is programmed to electrically connect atleast two electrodes to the sensing circuit. A cardiac signal is sensedafter the sensing circuit and the sense interface are programmed.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects of the invention will be apparent to persons skilled in the artupon reading and understanding the following detailed description andviewing the drawings that form a part thereof, each of which are not tobe taken in a limiting sense. The scope of the present invention isdefined by the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe similar components throughout the several views. The drawingsillustrate generally, by way of example, but not by way of limitation,various embodiments discussed in the present document. The drawing arefor illustrative purposes only and not to scale nor anatomicallyaccurate.

FIG. 1 is an illustration of an embodiment of a CRM system, including animplantable medical device and an external system, and portions of anenvironment in which it is used.

FIG. 2A is a block diagram illustrating one embodiment of portions ofthe circuit of the implantable medical device providing for wireless ECGsensing.

FIG. 2B is a block diagram illustrating another embodiment of portionsof the circuit of the implantable medical device providing for thewireless ECG sensing.

FIG. 3A is an illustration of one exemplary electrode system for thewireless ECG sensing.

FIG. 3B is an illustration of another exemplary electrode system for thewireless ECG sensing.

FIG. 3C is an illustration of another exemplary electrode system for thewireless ECG sensing.

FIG. 3D is an illustration of another exemplary electrode system for thewireless ECG sensing.

FIG. 3E is an illustration of another exemplary electrode system for thewireless ECG sensing.

FIG. 3F is an illustration of another exemplary electrode system for thewireless ECG sensing.

FIG. 3G is an illustration of an exemplary electrode system for multiplevector wireless ECG sensing.

FIG. 4 is a block diagram showing one embodiment of portions of thecircuit of the implantable medical device.

FIG. 5 is a block diagram showing one embodiment of portions of the CRMsystem including the implantable medical device and the external system.

FIG. 6 is a flow chart illustrating one embodiment of a method for awireless ECG sensing using an implantable medical device.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description provides examples,and the scope of the present invention is defined by the appended claimsand their equivalents.

It should be noted that references to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.

This document discusses a cardiac rhythm management (CRM) system thatprovides for sensing of a signal approximating the surface ECG using animplantable medical device, thus eliminating the need of attaching skincontact electrodes and the wires/cables connecting the electrodes and anECG recorder. Studies have shown signals sensed using electrodesimplanted in certain locations within a body approximate the surfaceECG, i.e., contain some or all of the information extractable from thesurface ECG. Such signals are usable for diagnostic and other purposesas a substitute for the surface ECG.

In this document, a “user” includes a physician or other caregiver usingthe CRM system to treat a patient. “Surface ECG” includes a cardiacelectrical signal sensed though electrodes attached to the skin surface.“Subcutaneous ECG” includes a cardiac electrical signal sensed thoughimplantable electrodes placed under the skin and is similar to thesurface ECG in terms of characteristics and diagnostic informationcontained. “Electrogram” includes a cardiac electrical signal sensedthough implantable electrodes placed in or on the heart. “Wireless ECG”includes a signal approximating the surface ECG, acquired without usingsurface (skin contact) electrodes.

FIG. 1 is an illustration of an embodiment of portions of a CRM system100 and portions of the environment in which system 100 is used. CRMsystem 100 includes an implantable system 115, an external system 155,and a telemetry link 145 providing for bidirectional communicationbetween implantable system 115 and external system 155. Implantablesystem 115 includes an implantable medical device 120 and a lead system108. Implantable medical device 120 is implanted within a body 102 andcoupled to a heart 105 via lead system 108. Examples of implantablemedical device 120 include, but are not limited to, pacemakers,pacemaker/defibrillators, cardiac resynchronization devices, cardiacremodeling control devices, and cardiac monitors. In one embodiment,lead system 108 includes multiple atrial and ventricular leads. In oneembodiment, external system 155 includes a programmer. In anotherembodiment, external system 155 is a patient management system includingan external device 150 in proximity of implantable device 140, a remotedevice 170 in a relatively distant location, and a telecommunicationnetwork 160 linking external device 150 and remote device 170. Thepatient management system allows access to implantable system 115 from aremote location, for purposes such as monitoring patient status andadjusting therapies. In one embodiment, telemetry link 145 is aninductive telemetry link. In an alternative embodiment, telemetry link145 is a far-field radio-frequency telemetry link. In one embodiment,telemetry link 145 provides for data transmission from implantablemedical device 120 to external system 155. This may include, forexample, transmitting real-time physiological data acquired byimplantable medical device 120, extracting physiological data acquiredby and stored in implantable medical device 120, extracting therapyhistory data stored in implantable medical device 120, and extractingdata indicating an operational status of implantable medical device 120(e.g., battery status and lead impedance). In a further embodiment,telemetry link 145 provides for data transmission from external system155 to implantable medical device 120. This may include, for example,programming implantable medical device 120 to acquire physiologicaldata, programming implantable medical device 120 to perform at least oneself-diagnostic test (such as for a device operational status), andprogramming implantable medical device 120 to deliver at least onetherapy.

FIG. 2A is a block diagram illustrating one embodiment of portions ofthe circuit of an implantable medical device 220A providing for wirelessECG sensing. Implantable medical device 220A is a specific embodiment ofimplantable medical device 120 and includes, among other components, aprogrammable sensing circuit 222 to sense a cardiac signal. Programmablesensing circuit 222 includes a pair of differential inputs, sense inputs223 and 224, to sense the cardiac signal through electrodes 210A and210B. Electrodes 210A and 210B are configured and placed in locationsselected for sensing a signal approximating the surface ECG in body 102.In one embodiment, programmable sensing circuit 222 is programmable fora frequency response suitable for sensing the wireless ECG. In oneembodiment, programmable sensing circuit 222 is programmable for atleast a frequency response suitable for sensing the wireless ECG andanother frequency response suitable for sensing an intracardiacelectrogram.

FIG. 2B is a block diagram illustrating another embodiment of portionsof the circuit of an implantable medical device 220B providing for thewireless ECG sensing. Implantable medical device 220B is anotherspecific embodiment of implantable medical device 120 and furtherincludes a programmable sense interface 230. Programmable senseinterface 230 includes a plurality of sense interface inputs and oneoutput connected to sense input 223 and another output connected tosense input 224. The sense interface inputs connect to a plurality ofelectrodes including electrodes 210A and 210B. Programmable senseinterface 230 provides for selective connections between any two of theplurality of electrodes to sense inputs 223 and 224. For example, duringone period of time, programmable sense interface 230 is programmed toconnect electrode 210A to sense input 223 and electrode 210B to senseinput 224; during another period of time, programmable sense interface230 is programmed to connect electrode 210M to sense input 223 andelectrode 210N to sense input 224. In general, electrodes 210A, 210B,210M, and 210N each refer to any one of a plurality of electrodesavailable in implantable system 115 for use for the wireless ECGsensing. Programmable sense interface 230 is programmable to connect afirst pair of electrodes to programmable sensing circuit 222 at onetime, a second pair of electrodes to programmable sensing circuit 222 atanother time, and so forth. If implantable medical device 220B includesa multi-channel sensing circuit, such as multiple units of programmablesensing circuit 222 in parallel, programmable sense interface 230 isprogrammable to connect multiple pairs of electrodes each to one sensingchannel to allow simultaneous sensing of multiple signals eachapproximating one surface ECG vector.

Implantable medical device 220B further includes a processor 232 tocontrol its operation. Processor 232 includes a command receiver 234 toreceive an ECG acquisition command and produces an ECG acquisitionsignal to start sensing the cardiac signal. The cardiac signal, i.e.,the signal approximating the surface ECG, is being sensed while the ECGacquisition signal is present in implantable medical device 220B. If theECG acquisition signal is present, programmable sensing circuit 222 andprogrammable sense interface 230 are both programmed for sensing thesignal approximating the surface ECG. The ECG acquisition command isgenerated either from external system 155 or from within implantablemedical device 220B. In one embodiment, a user causes the ECGacquisition command to be transmitted to implantable medical device 220Bwhen the surface ECG is needed. In another embodiment, processor 232includes a detector to detect a predetermined condition and produces theECG acquisition command when the predetermined condition is detected. Inone specific embodiment, the detector includes an arrhythmia detectorthat detects an arrhythmic episode from an electrogram. In anotherspecific embodiment, the detector includes an activity sensor such as anaccelerometer sensing the body's gross physical movements and arespiratory sensor sensing minute ventilation. In one specificembodiment, to acquire the signal approximating the surface ECG duringexercise, the detector produces the ECG acquisition command when thesensed activity level exceeds a predetermined threshold. Thus, the ECGacquisition is activated during exercise. In another embodiment, theactivity level is used to stop the acquisition of the signalapproximating the surface ECG when motion artifact on that signalbecomes a concern. In one specific embodiment, the detector detects thepredetermined condition and produces the ECG acquisition command on acontinuous basis. In another specific embodiment, the detector detectsthe predetermined condition and produces the ECG acquisition commandaccording to a built-in or user-programmable schedule, such as on anhourly, daily, weekly, or other periodic basis. In this embodiment,processor 232 includes a detection timer to activate and time thedetection of the predetermined condition according to the built-in oruser-programmable schedule.

In FIGS. 3A-F, various embodiments of electrodes 210A-B (or 210M-N) arereferenced as 210AA-BA, 210AB-BB, 210AC-BC, 210AD-BD, 210AE-BE, and210AF-BF. In one embodiment, to sense the signal approximating thesurface ECG, electrode 210A is electrically connected to sense input223, and electrode 210B is electrically connected to sense input 224,where electrodes 210A-B include one of electrode pairs 210AA-BA,210AB-BB, 210AC-BC, 210AD-BD, 210AE-BE, and 210AF-BF. In anotherembodiment, to sense the signal approximating the surface ECG,programmable sense interface 230 is programmed to provide an electricalconnection between electrode 210A and sense input 223 and anotherelectrical connection between electrode 210B and sense input 224, whereelectrodes 210A-210B include one of electrode pairs 210AA-BA, 210AB-BB,210AC-BC, 210AD-BD, 210AE-BE, and 210AF-BF. FIG. 3G illustrates anelectrode system allowing multiple signals each approximating onesurface ECG vector.

FIG. 3A is an illustration of one exemplary electrode system for thewireless ECG sensing. An implantable medical device 320A, which is aspecific embodiment of implantable medical device 120, is electricallyconnected to heart 105 through a lead system including, but not beinglimited to, leads 308A and 308B. Electrodes used for the wireless ECGsensing are selected from pacing electrodes of the lead system.

Implantable medical device 320A includes a hermetically sealed can 341to house its circuit. The circuit housed in can 341 includes at leastportions of programmable sensing circuit 222. Can 341 has an outersurface subject to contact with body tissue. Can 341 includes orprovides for a base of a can electrode 340. At least a portion of theouter surface of can 341 is made of electrically conductive material. Inone embodiment, can 341 is used as can electrode 340. In one specificembodiment, can electrode 340 includes at least one conductive portionof can 341. In another embodiment, can electrode 340 is incorporatedonto the outer surface of can 341. Can electrode 340 is electricallyinsulated from any conductive portion of can 341 using a non-conductivelayer. In one specific embodiment, a hermetically sealed feedthroughincluding a conductor provides for an electrical connection between canelectrode 340 and the circuit housed in can 341. A header 342 isattached to can 341 and includes connectors 343A-B providing forelectrical access to the circuit housed in can 341.

As illustrated in FIG. 3A, the lead system includes an atrial pacinglead 308A and a ventricular pacing lead 308B. Atrial pacing lead 308Ahas a proximal end 314A and a distal end 313A. Proximal end 314Aconnects to connector 343A. A tip electrode 312A is located in distalend 313A. A ring electrode 210AA is located near distal end 313A, at apredetermined distance from tip electrode 312A. Ventricular pacing lead308B has a proximal end 314B and a distal end 313B. Proximal end 314Bconnects to connector 343B. A tip electrode 312B is located in distalend 313B. A ring electrode 210BA is located near distal end 313B, at apredetermined distance from tip electrode 312B. In one specificembodiment, as illustrated in FIG. 3A, atrial pacing lead 308A is an RAlead, and ventricular pacing lead 308B is an RV lead. In anotherspecific embodiment, atrial pacing lead 308A is an RA lead, andventricular pacing lead 308B is an LV lead.

In one embodiment, to sense the signal approximating the surface ECG,the ring electrode of the RA lead (electrode 210AA) is electricallyconnected to sense input 223, and the ring electrode of the RV (or LV)lead (electrode 210BA) is electrically connected to sense input 224. Inanother embodiment, to sense the signal approximating the surface ECG,programmable sense interface 230 is programmed to provide an electricalconnection between the ring electrode of the RA lead (electrode 210AA)and sense input 223 and another electrical connection between the ringelectrode of the RV (or LV) lead (electrode 210BA) and sense input 224.

FIG. 3B is an illustration of another exemplary electrode system for thewireless ECG sensing. An implantable medical device 320B, which isanother specific embodiment of implantable medical device 120, iselectrically connected to heart 105 through the lead system includingleads 308A and 308B. The ring electrode of ventricular pacing lead 308Bis used as electrode 210AB, and can electrode 340 is used as electrode210BB, for sensing a signal approximating the surface ECG. In onespecific embodiment, as illustrated in FIG. 3B, ventricular pacing lead308B is an RV lead. In another specific embodiment, ventricular pacinglead 308B is an LV lead.

In one embodiment, to sense the signal approximating the surface ECG,the ring electrode of the RV (or LV) lead (electrode 210AA) iselectrically connected to sense input 223, and can electrode 340(electrode 210BA) is electrically connected to sense input 224. Inanother embodiment, to sense the signal approximating the surface ECG,programmable sense interface 230 is programmed to provide an electricalconnection between the ring of the RV (or LV) lead (electrode 210AA) andsense input 223 and another electrical connection between can electrode340 (electrode 210BA) and sense input 224.

FIG. 3C is an illustration of another exemplary electrode system for thewireless ECG sensing. Implantable medical device 320C is anotherspecific embodiment of implantable medical device 120. An electrode210AC is incorporated onto header 342. In one specific embodiment,implantable medical device 320C includes an impedance sensor functioningas a respiratory sensor sensing an impedance signal indicative of minuteventilation. Electrode 210AC is an indifferent electrode of theimpedance sensor. Can electrode 340 is used as electrode 210BC.

In one embodiment, to sense the signal approximating the surface ECG,electrode 210AC (e.g., the indifferent electrode of the impedancesensor) is electrically connected to sense input 223, and electrode210BC (can electrode 340) is electrically connected to sense input 224.In another embodiment, to sense the signal approximating the surfaceECG, programmable sense interface 230 is programmed to provide anelectrical connection between electrode 210AC (e.g., the indifferentelectrode of the impedance sensor) and sense input 223 and anotherelectrical connection between electrode 210BC (can electrode 340) andsense input 224.

In another embodiment, multiple electrodes are incorporated onto header342. Any of electrodes are either dedicated for sensing the signalapproximating the surface ECG or also used for other purposes. Any ofsuch electrodes can function as electrode 210AC.

FIG. 3D is an illustration of another exemplary electrode system for thewireless ECG sensing. Implantable medical device 320D is anotherspecific embodiment of implantable medical device 120. Concentricelectrodes are incorporated onto the outer surface of can 341. Theconcentric electrodes are insulated from the conductive portion of can341 with a non-conductive layer. As shown in FIG. 3D, the pair ofconcentric electrodes include an inner electrode 210AD and an outerelectrode 210BD. Inner electrode 210AD has a circular shape. Outerelectrode 210BD has a ring shape. In one embodiment, inner electrode210AD has a surface area of about 15 to 50 mm², and the outer electrodehas a surface area of about 50 to 150 mm². In one specific embodiment,inner electrode 210AD has a surface area of about 31.7 mm², and theouter electrode has a surface area of about 87.1 mm². In one embodiment,a hermetically sealed feedthrough including a conductor provides for anelectrical connection between inner electrode 210AD and the circuithoused in can 341, and another hermetically sealed feedthrough includinga conductor provides for another electrical connection between outerelectrode 210BD and the circuit housed in can 341. In anotherembodiment, a hermetically sealed feedthrough including two conductorsprovides for electrical access to the circuit housed in can 341 for bothinner electrode 210AD and outer electrode 210BD.

In one embodiment, to sense the signal approximating the surface ECG,inner electrode 210AD is electrically connected to sense input 223, andouter electrode 210BD is electrically connected to sense input 224. Inanother embodiment, to sense the signal approximating the surface ECG,programmable sense interface 230 is programmed to provide an electricalconnection between the inner electrode 210AD and sense input 223 andanother electrical connection between outer electrode 210BD and senseinput 224.

FIG. 3E is an illustration of another exemplary electrode system for thewireless ECG sensing. Implantable medical device 320E is anotherspecific embodiment of implantable medical device 120. A pair ofconcentric electrodes is incorporated (attached) onto the outer surfaceof can 341. The concentric electrodes are electrically insulated fromthe conductive portion of can 341 using a non-conductive layer. As shownin FIG. 3E, the pair of concentric electrodes includes an innerelectrode 210AE and an outer electrode 210BE. Inner electrode 210AE hasa circular shape. Outer electrode 210BE has a shape approximating thecontour of can 341. In one embodiment, inner electrode 210AE has asurface area of about 3 to 12 mm², and the outer electrode has a surfacearea of about 100 to 250 mm². In one specific embodiment, innerelectrode 210AE has a surface area of about 7.9 mm², and the outerelectrode has a surface area of about 170 mm². In one embodiment, ahermetically sealed feedthrough including a conductor provides for anelectrical connection between inner electrode 210AE and the circuithoused in can 341, and another hermetically sealed feedthrough includinga conductor provides for another electrical connection between outerelectrode 210BE and the circuit housed in can 341. In anotherembodiment, a hermetically sealed feedthrough including two conductorsprovides for electrical access to the circuit housed in can 341 for bothinner electrode 210AE and outer electrode 210BE.

In one embodiment, to sense the signal approximating the surface ECG,inner electrode 210AE is electrically connected to sense input 223, andouter electrode 210BE is electrically connected to sense input 224. Inanother embodiment, to sense the signal approximating the surface ECG,programmable sense interface 230 is programmed to provide an electricalconnection between inner electrode 210AE and sense input 223 and anotherelectrical connection between outer electrode 210BE and sense input 224.

FIG. 3F is an illustration of another exemplary electrode system for thewireless ECG sensing. Implantable medical device 320F is anotherspecific embodiment of implantable medical device 120. Implantablemedical device 320F includes an antenna 344 for radio-frequencytelemetry. Antenna 344 is electrically connected to the circuit housedin can 341. In one embodiment, as illustrated in FIG. 3F, antenna 344projects from header 342 and extends along one side of can 341. In oneembodiment, antenna 344 includes a metal conductor with a distal portionexposed for functioning as an antenna electrode 210AF. Can electrode 340is used as electrode 210BF.

In one embodiment, to sense the signal approximating the surface ECG,antenna 344/electrode 210AF is electrically connected to sense input223, and can electrode 340 is electrically connected to sense input 224.In another embodiment, to sense the signal approximating the surfaceECG, programmable sense interface 230 is programmed to provide anelectrical connection between antenna 344/electrode 210AF and senseinput 223 and another electrical connection between can electrode 340and sense input 224.

It is to be understood that the embodiments discussed with reference toFIGS. 3A-E are intended to be examples but not limitations. Otherelectrode configurations and selections are usable as long as theyprovide for sensing of signals that approximates the surface ECG orotherwise contains valuable information for diagnostic and/ortherapeutic purposes. In various embodiments in which multiple ECGvectors are needed, multiple pairs of electrodes are selected,simultaneously or one at a time, for a multi-channel wireless ECGsensing. In one specific embodiment, multiple signals are sensed toapproximate a standard multi-lead surface ECG recording. In anotherspecific embodiment, multiple signals are sensed based on needs ofspecific information for particular diagnostic purposes. The signals donot necessarily approximate standard surface ECG vectors.

FIG. 3G is an illustration of an exemplary electrode system allowingsuch multiple vector wireless ECG sensing. As illustrated in FIG. 3G,the electrode system includes all the electrodes discussed above withreference to FIGS. 3A-F. That is, the electrode system includes the tipand ring electrodes of an atrial lead (A-TIP and A-RING), the tip andring electrodes of one or more ventricular leads (V-TIP and V-RING), thecan of the implantable medical device (can electrode), one or moreelectrodes incorporated onto the header of the implantable medicaldevice (header electrodes), two or more concentric electrodes, and theantenna electrode. In one embodiment, to sense the signal approximatingthe surface ECG, programmable sense interface 230 is programmable toprovide an electrical connection between one of these electrodes andsense input 223 and another electrical connection between another one ofthese electrodes and sense input 224. In other words, programmable senseinterface 230 is programmable to provide electrode connection betweenprogrammable sensing circuit 222 and one pair of electrode selected fromany two electrodes available in implantable system 115. In oneembodiment, programmable sense interface 230 is programmed to connectseveral pairs of electrodes to programmable sensing circuit 222, one ata time, to obtain multiple signals (vectors). In another embodiment,programmable sense interface 230 is programmed to connect several pairsof electrodes each to one channel of a multi-channel sensing circuit(such as multiple units of programmable sensing circuit 222 inparallel), to obtain multiple signals (vectors) simultaneously. In theseembodiments, the pair or pairs of electrodes each include anycombination of the electrodes for sensing the signal approximating thesurface ECG, including electrodes 210AA-AF, electrodes 210BA-BF, and anyother electrodes in implantable system 115. In one specific embodiment,the implantable medical device includes the two (first and second)header electrodes and the can electrode for the wireless ECG sensing.ECG vectors are sensed between (1) the first and second headerelectrodes, (2) the first header electrode and the can electrode, and(3) the second header electrode and the can electrode. In anotherspecific embodiment, the implantable medical device includes one of theheader electrodes, the antenna electrode, and the can electrode for thewireless ECG sensing. ECG vectors are sensed between (1) the headerelectrode and the antenna electrode, (2) the header electrode and thecan electrode, and (3) the antenna electrode and the can electrode. Inanother specific embodiment, the implantable medical device includes thetwo (first and second) header electrodes, the antenna electrode, and thecan electrode for the wireless ECG sensing. ECG vectors are sensedbetween (1) the first and second header electrodes, (2) the first headerelectrode and the antenna electrode, (3) the first header electrode andthe can electrode, (4) the second header electrode and the antennaelectrode, (5) the second header electrode and the can electrode, and(6) the antenna electrode and the can electrode. Other specificembodiments involving any electrode combinations for the wireless ECGsensing will be employed based on possible diagnostic and other medicalneeds and considerations.

FIG. 4 is a block diagram showing one embodiment of portions of thecircuit of implantable medical device 120, including a programmablesense circuit 422, processor 232, an implant telemetry module 436, and amemory circuit 438.

Programmable sensing circuit 422, which is a specific embodiment ofprogrammable sensing circuit 222 includes inputs 223 and 224, apreamplifier circuit 425, a decimator 426, an analog-to-digitalconverter (ADC) 427, and a digital band-pass filter 428. In oneembodiment, preamplifier circuit 425 includes an analog amplifier and ananalog filter. In another embodiment, programmable sense interface 230includes the analog filter. Programmable sensing circuit 422 has a gainand a frequency response determined by the characteristics ofpreamplifier circuit 425 and digital band-pass filter 428. In oneembodiment, the gain and the frequency response of programmable sensingcircuit 422 are each programmable. The gain includes a gain programmablefor at least a gain selectable for being suitable for sensing a signalapproximating the surface ECG and a gain selectable for being suitablefor sensing intracardiac electrogram. The frequency response includes apass band programmable for at least a surface ECG pass band selectablefor being suitable for sensing a signal approximating the surface ECGand an intracardiac electrogram pass band selectable for being suitablefor sensing intracardiac electrogram. Each pass band is defined by a lowcutoff frequency and a high cutoff frequency. At least one of the lowcutoff frequency and the high cutoff frequency is programmable. The lowcutoff frequency and/or the high cutoff frequency are programmed byprogramming one or both of preamplifier circuit 425 and digitalband-pass filter 428. The surface ECG pass band includes a low cutofffrequency chosen to ensure that the interested low-frequency componentsare included in the sensed signal approximating the surface ECG. In oneembodiment, the low cutoff frequency of the surface ECG pass band isprogrammable for 4 Hz or less. In another embodiment, the low cutofffrequency of the surface ECG pass band is programmable to 0.5 Hz orless. In one embodiment, the low cutoff frequency for programmablesensing circuit 422 is programmable in a range of 0.1 Hz to 30 Hz, andthe high cut-off frequency for programmable sensing circuit 422 isprogrammable in a range of 30 Hz to 150 Hz. When the pass band isprogrammed to the surface ECG pass band, the low cutoff frequency isprogrammed to a value between 0.1 Hz to 4 Hz, and the high cut-offfrequency is programmed to a value between 30 Hz to 100 Hz. When thepass band is programmed to the intracardiac electrogram pass band, thelow cutoff frequency is programmed to a value between 10 Hz to 30 Hz,and the high cut-off frequency is programmed to a value between 60 Hz to150 Hz.

Implant telemetry module 436 transmits the sensed signal approximatingthe surface ECG to external system 155 via telemetry link 145. In oneembodiment, command receiver 234 receives the ECG acquisition commandfrom external system 155 through implant telemetry module 436.

Memory circuit 438 includes an ECG storage to store the sensed signalapproximating the surface ECG. In one embodiment, upon receiving the ECGacquisition command, implantable medical device 120 senses the signalapproximating the surface ECG and transmits the sensed signal toexternal system 155 in substantially real time. In another embodiment,upon receiving the ECG acquisition command, implantable medical device120 senses the signal approximating the surface ECG and stores thesensed signal in the ECG storage to be transmitted at a later time.

FIG. 5 is a block diagram showing portions of CRM system 100 includingelectrodes 210A and 210B, implantable medical device 120, and externalsystem 155. External system 155 includes, among other components, anexternal telemetry module 552, a user input device 554, and a display556. External telemetry module 552 receives the signal approximating thesurface ECG via telemetry link 145 from implantable medical device 120,and transmits the ECG acquisition command to implantable medical device120. User input device 554 receives the ECG acquisition command enteredby the user. Display 556 visually presents the signal approximating thesurface ECG. In one embodiment, the signal approximating the surface ECGis presented in substantially real time as it is being sensed byimplantable medical device 120. In another embodiment, the signalapproximating the surface ECG is displayed as it is extracted from theECG storage of memory circuit 438 in implantable medical device 120.

In one embodiment, external system 155 includes a programmer. In anotherembodiment, external system 155 is a patient management system includingexternal device 150, network 160, and remote device 170, as illustratedin FIG. 1. In one specific embodiment, remote device 170 includes userinput 554 and display 556. This allows the user to view either real timeor stored ECG of a patient from a remote facility.

FIG. 6 is a flow chart illustrating one embodiment of a method for awireless ECG sensing using a system such as CRM system 100 discussedabove. The method allows sensing of a signal substituting for a surfaceECG using an implantable medical device, eliminating the need for skincontact electrodes and wires/cables connecting the electrodes and an ECGrecording device.

An ECG acquisition command is received by the implantable medical deviceat 600. In one embodiment, the ECG acquisition command is received froman external device via telemetry. In another embodiment, one or morepredetermined cardiac conditions are detected by the implantable medicaldevice, and the ECG acquisition command is generated within theimplantable medical device in response to a detection of the one or morepredetermined cardiac conditions.

In response to the ECG acquisition command, a sensing circuit of theimplantable medical device is programmed for surface ECG monitoring at610. This includes programming a band-pass filtering circuit with cutofffrequencies suitable for the surface ECG monitoring. In one embodiment,the low cutoff frequency is programmed to a value between about 0.1 Hzand 10 Hz, and the high cutoff frequency is programmed to a valuebetween about 30 Hz and 100 Hz. In one specific embodiment, wheremaximum amount of information is desired, the low cutoff frequency isprogrammed to approximately 0.1 Hz, and the high cutoff frequency isprogrammed to approximately 100 Hz. In another specific embodiment,where the noise level is to be minimized, the low cutoff frequency isprogrammed to approximately 0.5 Hz, and the high cutoff frequency isprogrammed to approximately 50 Hz or less.

In response to the ECG acquisition command, a sense interface of theimplantable medical device is programmed to electrically connect a pairof electrodes to the sensing circuit at 620. The pair of electrodes issuitable for sensing a cardiac signal approximating the surface ECG. Inone embodiment, the sense interface is programmed for an electricalconnection between the sensing circuit and a ring electrode of an RApacing lead and another electrical connection between the sensingcircuit and a ring electrode of an RV pacing lead. In anotherembodiment, the sense interface is programmed for an electricalconnection between the sensing circuit and the ring electrode of the RVpacing lead and another electrical connection between the sensingcircuit and a housing of the implantable medical device. In anotherembodiment, the sense interface is programmed for an electricalconnection between the sensing circuit and an indifferent electrode ofan impedance sensor included in the implantable medical device andanother electrical connection between the sensing circuit and thehousing of the implantable medical device. In another embodiment, thesense interface is programmed for connections between the sensingcircuit and a pair of concentric electrodes incorporated onto thehousing of the implantable medical device. In one specific embodiment,the concentric electrodes include an inner electrode and an outerelectrode, and the sense interface is programmed for an electricalconnection between the sensing circuit and the inner electrode andanother electrical connection between the sensing circuit and the outerelectrode.

After the sensing circuit and the sense interface are programmed, thecardiac signal approximating the surface ECG is sensed at 630. In oneembodiment, the sensed cardiac signal is transmitted to the externaldevice for a substantially real time display. In another embodiment, thesensed cardiac signal is stored in the implantable medical device andtransmitted to the external device for display at a later time.

In one embodiment, the sensed cardiac signal approximating the surfaceECG is displayed for measurements related to fiducial points including,but are not limited to, P wave, QRS onset, R wave, QRS offset, and Twave. In one embodiment, the sensed cardiac signal approximating thesurface ECG is simultaneously displayed with the signals acquired by theimplantable medical device and/or derived from these acquired signals,such as sense markers indicative of intrinsic cardiac depolarizations,pace markers indicative of pacing pulse deliveries, a minute ventilationsignal, heart sounds, and markers indicative of respiratory and othermechanical events. In one embodiment, sensing the cardiac signalapproximating the surface ECG enhances an overall sensing scheme forpacing and/or defibrillation therapies. In one specific embodiment, thecardiac signal approximating the surface ECG provides an independentverification of events detected from an electrogram. In another specificembodiment, the cardiac signal approximating the surface ECG provides asubstitute for an electrogram in the event that the sensing system forthat electrogram dysfunctions. In one embodiment, where a patientmanagement system is used, the cardiac signal approximating the surfaceECG is displayed in real time for circadian events such as nocturnalatrial fibrillation or apnea. In one specific embodiment, these eventsare stored for trending purposes. The trending is used to determine anddisplay shifts in signal morphology over time.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. For example, the wireless ECGsensing system discussed above can be implemented in any implantablemedical device that includes a sensing circuit and electrodes suitablefor sensing a signal approximating the surface ECG. Other embodiments,including any possible permutation of the system components discussed inthis document, will be apparent to those of skill in the art uponreading and understanding the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

1. A cardiac rhythm management system comprising: a plurality ofimplantable electrodes including at least a first electrode and a secondelectrode selectable for sensing a cardiac signal approximating asurface electrocardiogram (ECG); and an implantable medical deviceincluding: a sensing circuit including: a first sense input and a secondsense input being a pair of differential inputs for sensing the cardiacsignal approximating the surface ECG; a gain programmable for at least asurface ECG gain selectable for sensing the cardiac signal approximatingthe surface ECG and an electrogram gain selectable for sensing anintracardiac electrogram; and a frequency response programmable for atleast a surface ECG pass band selectable for sensing the cardiac signalapproximating the surface ECG and an intracardiac electrogram pass bandselectable for sensing an intracardiac electrogram; a processor tocontrol the operation of the sensing circuit, the processor including acommand receiver to receive an ECG acquisition command; and aprogrammable sense interface providing at least a first electricalconnection and a second electrical connection in response to the ECGacquisition command, the first electrical connection connecting thefirst electrode to the first sense input, the second electricalconnection connecting the second electrode to the second sense input. 2.The system of claim 1, wherein the surface ECG pass band comprises a lowcutoff frequency programmable for 4 Hz or less.
 3. The system of claim2, wherein the low cutoff frequency of the surface ECG pass band isprogrammable for a value between about 0.1 Hz to 0.5 Hz.
 4. The systemof claim 2, wherein the surface ECG pass band comprises a high cutofffrequency programmable for 50 Hz or less.
 5. The system of claim 1,wherein the frequency response comprises a low cutoff frequency and ahigh cutoff frequency, wherein at least one of the low cutoff frequencyand the high cutoff frequency is programmable.
 6. The system of claim 5,wherein the low cutoff frequency is programmable in a range of about 0.1Hz to 30 Hz.
 7. The system of claim 5, wherein the high cutoff frequencyis programmable in a range of 30 Hz to 150 Hz.
 8. The system of claim 1,further comprising: a first pacing lead including a first proximal endand a first distal end; and a second pacing lead having a secondproximal end and a second distal end, wherein the first electrode is ator near the first distal end and the second electrode is at or near thesecond distal end.
 9. The system of claim 8, wherein: the first pacinglead is an atrial pacing lead; and the second pacing lead is aventricular pacing lead.
 10. The system of claim 9, wherein theventricular pacing lead comprises a right ventricular lead.
 11. Thesystem of claim 9, wherein the ventricular pacing lead comprises a leftventricular lead.
 12. The system of claim 9, wherein: the first pacinglead includes at least a first tip electrode and a first ring electrode,the first tip electrode located at the first distal end, the first ringelectrode located near the first distal end at a predetermined distancefrom the first tip electrode; and the second pacing lead includes atleast a second tip electrode and a second ring electrode, the second tipelectrode located at the second distal end, the second ring electrodelocated near the second distal end at a predetermined distance from thesecond tip electrode, wherein the first electrode is the first ringelectrode and the second electrode is the second ring electrode.
 13. Thesystem of claim 1, further comprising: a pacing lead including aproximal end and a distal end; a hermetically sealed can to house acircuit including at least portions of the sensing circuit; and a canelectrode including one of at least a portion of the can and anelectrode incorporated onto, and electrically insulated from, the can,wherein the first electrode is at or near the distal end of the pacinglead and the second electrode is the can electrode.
 14. The system ofclaim 13, wherein the pacing lead is a ventricular pacing lead.
 15. Thesystem of claim 14, wherein the pacing lead includes at least one tipelectrode and one ring electrode, the tip electrode located at thedistal end, the ring electrode located near the distal end at apredetermined distance from the tip electrode, wherein the firstelectrode is the ring electrode.
 16. The system of claim 1, wherein theimplantable medical device comprises a hermetically sealed can to housean implant circuit including at least portions of the sensing circuit.17. The system of claim 16, wherein the implantable medical devicecomprises a header attached to the can, the header including connectorsproviding for electrical access to the implant circuit.
 18. The systemof claim 17, wherein the implantable medical device comprises: at leastone header electrode being an electrode incorporated onto the header;and a can electrode including one of at least a portion of the can andan electrode incorporated onto, and electrically insulated from, thecan, wherein the first electrode is the at least one header electrodeand the second electrode is the can electrode.
 19. The system of claim18, wherein the implantable medical device comprises an impedancesensor, and wherein the at least one header electrode comprises anindifferent electrode of the impedance sensor.
 20. The system of claim19, wherein the impedance sensor is a respiratory sensor sensing aminute ventilation.
 21. The system of claim 17, wherein the implantablemedical device comprises: a telemetry antenna; and a can electrodeincluding one of at least a portion of the can and an electrodeincorporated onto, and electrically insulated from, the can, wherein thefirst electrode includes at least a portion of the telemetry antennafunctions and the second electrode is the can electrode.
 22. The systemof claim 21, wherein the telemetry antenna projects from the header andextends along a portion of the can.
 23. The system of claim 17, whereinthe can comprises an outer surface, and wherein the first electrode andthe second electrode comprise two concentric electrodes incorporatedonto the outer surface of the can.
 24. The system of claim 23, whereinthe at least two concentric electrodes comprise an inner electrode andan outer electrode, wherein the first electrode is the inner electrodeand the second electrode is the outer electrode.
 25. The system of claim23, wherein the inner electrode includes a circular shaped electrode,and outer electrode includes a ring shaped electrode.
 26. The system ofclaim 23, wherein the inner electrode includes a circular shapedelectrode, and outer electrode includes an electrode approximating acontour of the can.
 27. The system of claim 1, wherein the processorcomprises a detector to detect a predetermined condition and producesthe ECG acquisition command when the predetermined condition isdetected.
 28. The system of claim 27, wherein the processor furthercomprises a detection timer coupled to the detector, the detection timeractivating and timing the detection of the predetermined condition basedon a built-in or programmable schedule.
 29. The system of claim 1,further comprising an external system communicatively coupled to theimplantable medical device via telemetry, the external system includinga user input device to receive the ECG acquisition command.
 30. Thesystem of claim 29, wherein the implantable medical device comprises animplant telemetry module to transmit the sensed cardiac signal out ofthe implantable medical device and a memory circuit including an ECGstorage to store the sensed cardiac signal, and wherein the externalsystem comprises an external telemetry module to receive the sensedcardiac signal and a display to visually present the sensed cardiacsignal.
 31. The system of claim 30, wherein the external systemcomprises a programmer.
 32. The system of claim 30, wherein the externalsystem comprises a patient management system including: an externaldevice communicatively coupled to the implantable medical device viatelemetry; a network coupled to the external device; and a remote devicecoupled to the network.
 33. The system of claim 32, wherein the remotedevice comprises the user input device and the display.
 34. Animplantable medical device comprising: a sensing circuit programmablefor a frequency response suitable for sensing a surfaceelectrocardiogram (ECG), the sensing circuit including a first senseinput and a second sense input being a pair of differential inputs forsensing a cardiac signal; a hermetically sealed can to house an implantcircuit including at least portions of the sensing circuit, the canhaving an outer surface subject to contact with body tissue; and atleast two concentric electrodes incorporated onto the outer surface ofthe can, the at least two concentric electrodes including an innerelectrode and an outer electrode, wherein the inner electrode is coupledto the first sense input, and the outer electrode is coupled to thesecond sense input.
 35. The implantable medical device of claim 34,further comprising a processor to control the operation of the sensingcircuit, the processor including a command receiver to receiver an ECGacquisition command and produces an ECG acquisition signal to startsensing the cardiac signal.
 36. The implantable medical device of claim35, further comprising a programmable sense interface providingelectrical connections between the inner electrode and the first senseinput and between the outer electrode and the second sense input whenthe ECG acquisition signal is present.
 37. The implantable medicaldevice of claim 34, wherein the inner electrode includes a circularshaped electrode, and outer electrode includes a ring shaped electrode.38. The implantable medical device of claim 37, wherein the innerelectrode has a surface area of about 15 to 50 squared millimeters, andthe outer electrode has a surface area of about 50 to 150 squaredmillimeters.
 39. The implantable medical device of claim 34, wherein theinner electrode includes a circular shaped electrode, and outerelectrode includes an electrode approximating a contour of the can. 40.The implantable medical device of claim 39, wherein the inner electrodehas a surface area of about 3 to 12 squared millimeters, and the outerelectrode has a surface area of about 100 to 250 squared millimeters.41. The implantable medical device of claim 34, wherein the sensingcircuit comprises a band-pass filter having a surface ECG pass bandhaving a programmable low cutoff frequency and a programmable highcutoff frequency.
 42. The implantable medical device of claim 41,wherein the low cutoff frequency of the surface ECG pass band isprogrammable to a value between about 0.1 Hz to 0.5 Hz.
 43. Theimplantable medical device of claim 41, wherein the high cutofffrequency of the surface ECG pass band is programmable to 50 Hz or less.44. A cardiac rhythm management system comprising: a plurality ofimplantable electrodes configured for sensing cardiac signals eachapproximating a surface electrocardiogram (ECG) vector; and animplantable medical device including: a sensing circuit including aplurality of sensing channels providing for simultaneous sensing of thecardiac signals; a processor to control the operation of the sensingcircuit, the processor including a command receiver to receive an ECGacquisition command; and a programmable sense interface providing aplurality of pairs of electrical connections, each pair between one ofthe plurality of sensing channels and two electrodes selected from theplurality of implantable electrodes, wherein the plurality ofimplantable electrodes are incorporated onto the implantable medicaldevice.
 45. The system of claim 44, wherein the implantable medicaldevice comprises: a hermetically sealed can to house an implant circuitincluding at least portions of the sensing circuit; and a can electrodeincluding one of at least a portion of the can and an electrodeincorporated onto, and electrically insulated from, the can.
 46. Thesystem of claim 45, wherein the implantable medical device comprises aheader attached to the can, the header including connectors providingfor electrical access to the circuit.
 47. The system of claim 46,wherein the implantable medical device further comprises at least afirst header electrode being a first electrode incorporated onto theheader.
 48. The system of claim 47, wherein the implantable medicaldevice further comprises a second header electrode being a secondelectrode incorporated onto the header.
 49. The system of claim 48,wherein the programmable sensing circuit includes two or more of first,second, and third sensing channels, and wherein the programmable senseinterface is adapted to provide for two or more of a first pair ofelectrical connections connecting the first and second header electrodesto the first sensing channel, a second pair of electrical connectionsconnecting the first header electrode and the can electrode to thesecond sensing channel, and a third pair of electrical connectionsconnecting the second header electrode and the can electrode to thethird sensing channel.
 50. The system of claim 47, wherein theimplantable medical device further comprises a telemetry antenna, andwherein at least a portion of the telemetry antenna functions as anantenna electrode.
 51. The system of claim 50, wherein the telemetryantenna projects from the header and extends along a portion of the can.52. The system of claim 50, wherein the programmable sensing circuitincludes two or more of first, second, and third sensing channels, andwherein the programmable sense interface is adapted to provide for twoor more of a first pair of electrical connections connecting the firstheader electrode and the antenna electrode to the first sensing channel,a second pair of electrical connections connecting the first headerelectrode and the can electrode to the second sensing channel, and athird pair of electrical connections connecting the antenna electrodeand the can electrode to the third sensing channel.
 53. The system ofclaim 50, wherein the implantable medical device further comprises asecond header electrode being a second electrode incorporated onto theheader, and wherein the programmable sensing circuit includes two ofmore of first, second, third, fourth, fifth, and sixth sensing channels,and wherein the programmable sense interface is adapted to provide fortwo or more pairs of a first pair of electrical connections connectingthe first header electrode and the second header electrode to the firstsensing channel, a second pair of electrical connections connecting thefirst header electrode and the antenna electrode to the second sensingchannel, a third pair of electrical connections connecting the firstheader electrode and the can electrode to the third sensing channel, afourth pair of electrical connections connecting the second headerelectrode and the antenna electrode to the fourth sensing channel, afifth pair of electrical connections connecting the second headerelectrode and the can electrode to the fifth sensing channel, and asixth pair of electrical connections connecting the antenna electrodeand the can electrode to the sixth sensing channel.
 54. The system ofclaim 44, wherein the sensing channels each comprises a band-pass filterhaving a surface ECG pass band having a low cutoff frequency and a highcutoff frequency.
 55. The system of claim 54, wherein the low cutofffrequency of the surface ECG pass band is programmable to a valuebetween about 0.1 Hz to 0.5 Hz.
 56. The system of claim 54, wherein thehigh cutoff frequency of the surface ECG pass band is programmable to 50Hz or less.
 57. A method for acquiring a signal approximating a surfaceelectrocardiogram (ECG) using an implantable medical device, the methodcomprising: receiving an ECG acquisition command; programming a passband of a sensing circuit of the implantable device after receiving theECG acquisition command, the sensing circuit programmable for at least asurface ECG pass band and an intracardiac electrogram pass band, theprogramming including programming the pass band to the surface ECG passband; programming a sense interface of the implantable device toelectrically connect at least two implantable electrodes to the sensingcircuit after receiving the ECG acquisition command; and sensing acardiac signal after the programming the sensing circuit and theprogramming the sense interface.
 58. The method of claim 57, whereinreceiving the ECG acquisition command comprises receiving the ECGacquisition command from an external device via telemetry.
 59. Themethod of claim 57, wherein receiving the ECG acquisition commandcomprises: detecting a predetermined condition; and generating the ECGacquisition command in response to a detection of the predeterminedcondition.
 60. The method of claim 59, wherein detecting thepredetermined condition comprises detecting an arrhythmia.
 61. Themethod of claim 59, wherein detecting the predetermined conditioncomprises sensing an activity level.
 62. The method of claim 59, whereindetecting the predetermined condition comprises detecting thepredetermined condition according to a predetermined schedule.
 63. Themethod of claim 62, wherein detecting the predetermined conditioncomprises detecting the predetermined condition on a predeterminedperiodic basis.
 64. The method of claim 57, wherein programming thesensing circuit comprises programming a band-pass filter providing forthe pass band.
 65. The method of claim 57, wherein programming the passband comprises programming a low cutoff frequency to about 0.1 Hz. 66.The method of claim 57, wherein programming the pass band comprisesprogramming a low cutoff frequency to about 0.5 Hz.
 67. The method ofclaim 57, wherein programming the pass band comprises programming a highcutoff frequency to about 100 Hz.
 68. The method of claim 57, whereinprogramming the pass band comprises programming a high cutoff frequencyto about 50 Hz or less.
 69. The method of claim 57, further comprisingprogramming a gain of the sensing circuit after receiving the ECGacquisition command, the sensing circuit programmable for at least asurface ECG gain and an intracardiac electrogram gain, the programmingincluding programming the gain to the surface ECG gain.
 70. The methodof claim 57, wherein programming the sense interface comprisesprogramming the sense interface to electrically connect at least twoelectrodes selected from a plurality of implantable electrodes to thesensing circuit, the plurality of electrodes including at least two ormore of: a ring electrode of an atrial pacing lead; a ring electrode ofan ventricular pacing lead; one or more electrodes incorporated into aheader of the implantable medical device; a can electrode including oneof at least a portion of a conductive can housing electronics of theimplantable medical device and an electrode incorporated onto, andelectrically insulated from, the conductive can; a portion of an antennaproviding for radio-frequency telemetry for the implantable medicaldevice; an inner electrode of a plurality of concentric electrodesincorporated onto the conductive can; and one or more outer electrodesof the plurality of concentric electrodes incorporated onto theconductive can.
 71. The method of claim 57, wherein: programming thepass band comprises programming a plurality of sensing channels eachprogrammable for at least the surface ECG pass band and the intracardiacelectrogram pass band, the programming including programming the passband of each of the plurality of sensing channels to the surface ECGpass band; and programming the sense interface comprises programming thesense interface to electrically connect a plurality of electrode pairseach to one of the plurality of sensing channels after receiving the ECGacquisition command; and further comprising sensing the cardiac signaland one or more additional cardiac signals each approximating a vectorof the surface ECG after the programming the sensing circuit and theprogramming the sense interface.
 72. The method of claim 71, whereinprogramming the sense interface comprises programming the senseinterface to electrically connect the plurality of electrode pairs eachto one of the plurality of sensing channels, the plurality of electrodepairs selected from plurality of electrodes including at least three ormore of: one or more electrodes incorporated into a header of theimplantable medical device; a can electrode including one of at least aportion of a conductive can housing electronics of the implantablemedical device and an electrode incorporated onto, and electricallyinsulated from, the conductive can; and a portion of an antennaproviding for radio-frequency telemetry for the implantable medicaldevice.
 73. The method of claim 72, wherein programming the senseinterface comprises programming the sense interface to electricallyconnect the plurality of electrode pairs each to one of the plurality ofsensing channels, the plurality of electrode pairs selected fromplurality of electrodes including at least three or more of: a ringelectrode of an atrial pacing lead; a ring electrode of an ventricularpacing lead; one or more electrodes incorporated into a header of theimplantable medical device; a can electrode including one of at least aportion of a conductive can housing electronics of the implantablemedical device and an electrode incorporated onto, and electricallyinsulated from, the conductive can; a portion of an antenna providingfor radio-frequency telemetry for the implantable medical device; aninner electrode of a plurality of concentric electrodes incorporatedonto the conductive can; and one or more outer electrodes of theplurality of concentric electrodes incorporated onto the conductive can.74. The method of claim 57, further comprising storing the sensedcardiac signal in the implantable medical device.
 75. The method ofclaim 57, further comprising: transmitting the sensed cardiac signal toan external system for real time display; and displaying the sensedcardiac signal in real time.